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arXiv · 1512.04645

Dark matter search project PICO-LON

K. Fushimi·H. Ejiri·R. Hazama·H. Ikeda·K. Imagawa·K. Inoue·G. Kanzaki·A. Kozlov·R. Orito·T. Shima·Y. Takemoto·Y. Teraoka·S. Umehara·K. Yasuda·S. Yoshida
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Abstract

The PICO-LON project aims at search for cold dark matter by means of highly radio-pure and large volume NaI(Tl) scintillator. The NaI powder was purifed by chemical processing to remove lead isotopes and selecting a high purity graphite crucible. The concentrations of radioactive impurities of $^{226}$Ra and $^{228}$Th were effectively reduced to 58$\pm$4 $μ$Bq/kg and 1.5$\pm$1.9 $μ$Bq/kg, respectively. It should be remarked that the concentration of $^{210}$Pb, which is crucial for the sensitivity to dark matter, was reduced to 24$\pm$2 $μ$Bq/kg. The total background rate at 10 keVee was as low as 8 keV$^{-1}$kg$^{-1}$day$^{-1}$, which was sufficiently low to search for dark matter. Further purification of NaI(Tl) ingot and future prospect of PICO-LON project is discussed.

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K. Fushimi, H. Ejiri, R. Hazama, H. Ikeda, K. Imagawa, K. Inoue, G. Kanzaki, A. Kozlov, R. Orito, T. Shima, Y. Takemoto, Y. Teraoka, S. Umehara, K. Yasuda, S. Yoshida. 2015-12-15. Dark matter search project PICO-LON. https://doi.org/10.1088/1742-6596%2F718%2F4%2F042022

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